Check for ARM compiler in addition to clang (#10280)
Check for ARM compiler in addition to clang (#10280)

Add "-rtlib=compiler-rt" to CFLAGS when building with either Clang or
the ARM compiler.

Refs #10279
iulian787/spack,iulian787/spack,iulian787/spack,LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack,iulian787/spack,iulian787/spack